Overview

A HUB-ee wheel with a 120:1 gear reduction, M3 metric mounting threads and BMS-S PCB so it has an on board motor driver and quadrature encoder. Also available with 180:1 gear reduction as well as with an imperial mounting version.

Dimensions: 60mm overall diameter including tyre x 20mm wide.

Supplied fully assembled and tested - A MicroMatch connecting cable is NOT included but is available from our IDC connectors section with a choice of 3 lengths.

Controlling the BMS-S Wheel

The picture below illustrates what signals you need to send in order to turn the wheel – as a basic rule, send a PWM signal to the PWM pin (kinda obvious) then use the IN1 and IN2 pins to control direction – pull one high and the other low to move in one direction, reverse them for the other. The brake mode (when both IN1 and IN2 are high) will short circuit the motor coils, forcing the wheel to stop quickly and resist movement. The Stop – No Brake mode disconnects the motor and allows it to free-wheel a little.

Wheel Performance (these are approximate)

Sensors

What the sensors do

The wheel has a pair of reflective optical sensors that shine on a code disk in the outer rim of the wheel. Called a Quadrature Encoder, these sensors pick up the black and white alternating pattern of the code disk as the wheel turns and convert it into electrical pulses. Because of the positions of the sensors relative to the black and white stripes the two electrical outputs will produce pulses in a particular pattern that depends on the direction of the wheel – To cut a long story short, you can use a microcontroller to read the direction and speed of the wheel, and with a bit of clever control theory (A PID control loop) you can exercise some fairly precise control how fast the wheel is moving along with keeping track of how far the wheel has moved.

For more information on Quadrature encoders and PID control, start with these Wikipedia pages:

Attaching HUB-ee wheels to other things

Each wheel has a pair of metal threaded inserts inside so you can bolt it onto things securely; these will either have a metric M3 thread, or an imperial 4/40 thread, depending on the one you bought. These can be removed and replaced if you want. The bolt holes are also designed to accept the tip of a LEGO axle so you can incorporate it into your favourite LEGO creations.

The threaded inserts are 8mm long and sit in the centre of the wheel, that means that any screw you use has to go in 6mm deep before it will engage with the thread – for example, if you want to bolt the wheel to a 3mm thick piece of plastic then you are going to need a screw that is around 12mm long.

Take care when bolting the wheel – try not to over tighten the screws – the current design is not quite as strong as we wanted where the inserts are so if you over tighten the screws you can cause some minor damage to the insides – fortunately not enough to stop the wheel working!

Each wheel also comes with a handy right angle bracket designed to make it easy to attach to a flat chassis – ok, we lied a bit, the bracket is *almost* right angle (actually 89 degrees) thanks to the requirement for it to come out of the mould easily. It has a pair of slots so you can put bolts inside and have something to screw a screw into, these slots will take a metric M3 bolt, or a small 4/40 bolt (Some 4/40 bolts are too large)

The screws that go in at the top, through the nuts (see pic above), will press up against the screws that bolt the bracket to the wheel if they go in too far.

As an alternative mounting solution for people who prefer imperial screws you can always try this metal bracket.

Manufacturer's Details

Manufacturer:
Creative Robotics

Manufacturer's SKU:
HUB-ee 6020 BMDS 120 MET

02/05/2013, 17:08

"Gerry,

You are welcome."

– Admin

02/05/2013, 16:59

"Great advice - thanks.
I have discovered that the sub-min pololu motor 1451-315 is an exact fit for the wheel. As I already had one of these I installed it in the wheel and it worked perfectly! The gear ratio is different but still seems fine. I will take your advice and obtain a second battery NiMH 9.6V as you suggest and get another pololu motor (when I can afford them!!)
Your detailed comments are most appreciated."

– Gerry Curtis

02/05/2013, 07:47

"Gerry,

Leaving the motor in circuit can increase the force needed to spin by hand because is some designs of speed controller, the motor is effectively shorted by the MOSFET transistors when powered down. Not sure if that is the case with this particular design.

Not all of the supply voltage reaches the motor as some is lost through the MOSFET transistors but most in modern designs, these losses are small.

We will speak to the manufacturer about spare motors. I would also recommend that you move away from SLA batteries because of the voltage and in your case, the weight as well. Use 9.6V worth of NiMH or even LiPo. It will save the weight of about 1kg and drive the motor at a lower voltage. Also, SLA are not 'efficient' at fast discharges as the capacity is only about 40-60% of the rated Ah with full discharges below 1 hour. You may well find that with NiMH, the performance is similar to what you get now but with a significantly lower demand on the motors. I would suggest 2.2Ah NiMH battery pack at 9.6V for your application. "

– Admin

01/05/2013, 16:24

"Hi - thanks for all your advice. I have taken one of the motors apart and there is no visible damage but the motor had seized. The gearbox is fine. With the gearbox off I can just turn the motor by hand but it is fairly stiff.
Should I unsolder it from the board before testing?
Does the controller pass all the supply voltage to the motor?
Can you supply replacement motors? It looks a straightforward job to replace it if the controller board is still good.
I notice that the manufacturing company has them on their website but do not supply direct."

– Gerry Curtis

01/05/2013, 11:31

"Gerry,

This is a relatively new product to the market and we have not had a play with them ourselves yet. However, I would suggest that your vehicle weight is rather high for such a small drive. Also, a fully charged SLA battery can be as high as 14.7V which exceeds the maximum rating for these wheels.

It is not that common for motor speed controllers to have current limit protection although they do exist. When protection is provided, it would be mentioned in the specification. Fuses are not guaranteed to help as their time / current profile is often too slow to prevent damage to the controller and / or motor.

With your over voltage, the high vehicle weight, motor stall current is going to be very high. This could lead to a damaged gearbox due to the stall torque or the windings burning out due to the stall torque.

They would be repairable but whether it is cost effective is unknown. I suggest taking the wheels apart and seeing if the damage is obvious.

These wheels are sold as a component for incorporating into a customers own design and thus require the customer to exercise product constraints into their design. We are always on hand to give advice when requested.

Let us know what you find when opening it up and we can take it from there."

– Admin

01/05/2013, 10:30

"In answer to your questions:
The vehicle may have stalled briefly before I switched the power off.
The vehicle weighs 2.8 kg
The battery is a 12V 2.8AH sealed lead acid.
The had been running ok since purchase a few weeks ago.
There is no warning on your website about being no overload protection.
Do they have any internal fuses?
Are they repairable?
"

– Gerry Curtis

01/05/2013, 08:36

"Gerry,

They both locked up at exactly the same time! Does not sound like a manufacturing defect.

Was the vehicle stalled or under excessive load when they failed?
What is the vehicle weight?
What type of battery is it?
How long had they run for since you purchased them?"

– Admin

30/04/2013, 23:02

"I have two of these wheels that were working properly on a 12V battery supply, controlled by a Gertboard/Raspberry pi when suddenly they both locked up and now refuse to work. (Battery recharged and program checked.) The wheels are now locked and cannot be turned by hand even when disconnected. Are they burned out? Can they be repaired?"